Selective laser melting of hypereutectic Al-Si40-powder using ultra-short laser pulses

Abstract

We investigate the use of ultra-short laser pulses for the selective melting of Al-Si40-powder to fabricate complex lightweight structures with wall sizes below 100 μm combined with higher tensile strength and lower thermal expansion coefficient in comparison to standard Al-Si alloys. During the cooling process using conventional techniques, large primary silicon particles are formed which impairs the mechanical and thermal properties. We demonstrate that these limitations can be overcome using ultra-short laser pulses enabling the rapid heating and cooling in a non-thermal equilibrium process. We analyze the morphology characteristics and micro-structures of single tracks and thin-walled structures depending on pulse energy, repetition rate and scanning velocity utilizing pulses with a duration of 500 fs at a wavelength of 1030 nm . The possibility to specifically change and optimize the microstructure is shown.

Investigation into Additive Manufacturing for Controlling Thermal Expansion in Optical Applications

“…This also agrees with literature on LPBF that indicates most metallic material, including Al-Si alloys, processed with LPBF have a finer microstructure due to the high cooling rates [48], [50]- [53]. The finer microstructure leads to a higher hardness with most materials processed by LPBF, including Al-Si alloys [186], [188], [189]. The relationship between laser exposure time or laser scanning speeds on microstructure is related to the cooling rates, a faster scanning speed will increase cooling rate, and therefore create a finer microstructure.…”

Study of the Processing Conditions for Stainless Steel Additive Manufacturing Using Femtosecond Laser

“…2. The size of the particles was selected based on two aspects: a. the size of the spot diameter, so it can cover the maximum grain surface; b. the values found in literature, which were below 50 µm [60,62,63]. The chemical composition of these powders is presented in the following table (Table 1), which corresponds to an AISI 316L stainless steel.…”

“…Previous studies have demonstrated that the heat accumulation and melting of metal powders (such as iron [60], tungsten [60,61], copper [62] and aluminum [63]) is a feasible phenomenon when using USP lasers. These studies demonstrate that it is possible to melt various kinds of materials when laser pulses are consecutive enough, accumulating heat and increasing the temperature up to the melting threshold.…”

Additive Manufacturing (AM) for Advanced Materials and Structures

“…At present, due to the shortcomings of poor surface finish, low productivity, poor quality control, unrepeatability, limited component size, and limited range of printable materials, only a few AM processes are used in modern manufacturing [69]. For metal materials, various alloys have been proposed [16,70,71]. However, in actual production, the mismatch of material with different cooling rate or thermal expansion coefficient will cause many problems, such as peeling of different layers, thermal effects caused by high power, ablation of low melting point materials on the base layer, and different types problems caused by the formation and distribution of crystal images.…”